I think there’s a difference between “important” and “advanced.” Practicing deep meditation is both highly important and highly advanced.
Why spending so much time teaching something that is not doable per se?
Because this is the Buddha’s path—ethics, immersion, wisdom. The Buddha frequently taught immersion+ to lay people. Ajahn Brahm compares teaching advanced teachings with planting seeds. People will not understand it now and might even rebel against it, but it will help them later on. And of course, the more fundamental teachings are also taught. It doesn’t have to be either/or.